Diabetic Eye Disease

Diabetes mellitus is a disease which affects the body's ability to use and store sugar properly resulting in high blood glucose (sugar) levels. It is fast becoming an epidemic worldwide and in Malaysia, nearly 1.2 million people have diabetes. Diabetes is a chronic disease and it has widespread effects on the body’s organ systems with the eye being one of them.

Diabetic retinopathy is a disease of the retinal blood vessels and is the leading cause of blindness in adults between the ages of 25 to 74 years. Each year in Malaysia, anywhere between 15000 to 39000 people lose their sight because of complications from diabetes. The longer that someone has diabetes, the more likely they are to develop some degree of retinopathy and a proportion of these patients are at risk of blindness.

Non-proliferative diabetic retinopathy is an earlier stage of diabetic retinopathy and usually progresses slowly over the years. There can be mild, moderate or severe non-proliferative retinopathy depending on the amount of blood spots or fatty deposits leaking from the retinal blood vessels. The majority of patients do not develop significant loss of vision from non-proliferative retinopathy.

When retinopathy reaches the severe stage, there is a significant risk of progression to proliferative disease therefore, close monitoring of patients with diabetes is always important.

Non-proliferative retinopathy

Dot and blot haemorrhages in the earlier stages of diabetic retinopathy

Proliferative retinopathy develops as a progression from non-proliferative retinopathy and is responsible for most of the visual loss in diabetes. Abnormal new blood vessels grow (proliferate) on the surface of the retina and optic nerve and these fragile blood vessels tend to rupture and bleed into the vitreous cavity. When bleeding occurs, the patient can experience a sudden loss of vision with no associated pain. As the blood gets reabsorbed, scar tissue is formed on the surface of the retina and these tissues will eventually contract and pull on the retina causing a retinal detachment and further loss of vision.

These abnormal new vessels can also grow on the iris and cause a form of glaucoma, which itself can lead to blindness.

Proliferative Retinopathy

Formation of ‘new vessels’ (near optic disc) which are prone to bleeding

Visual loss with sudden bleeding (vitreous haemorrhage)

The macula is the most important part of the retina as it is responsible for 90% of our functional vision. Diabetic maculopathy is another subset of diabetic eye disease which can result in significant visual loss.

In the majority of cases, there is leakage of fluid and proteins from the small blood vessels in the macula and this results in oedema (swelling) and subsequent loss of central vision. In some patients, there is a shutdown of these small blood vessels altogether and the resulting ischaemia (lack of blood supply) to the macula results in irreversible visual loss.

Diabetic Maculopathy

Leakage of fluid and proteins causing swelling at the macula

Photographs of the retina are often taken for monitoring purposes and special investigations are done to evaluate the severity of retinopathy. One such investigation which is very helpful in detecting early effects of diabetic retinopathy is known as fundus flourescein angiography (FFA). The procedure involves injection of an orange dye into a vein in the arm and as this dye is transported to the eye, photographs of the retina are taken, showing any areas of leakage or poor blood flow. This can often reveal abnormalities which are not visible to the examining ophthalmologist. Another useful investigation is optical coherence tomography (OCT) which uses a very sophisticated laser to take high resolution cross section images of the retina.

Diagnosis and imaging

FFA(left) and OCT(right) being done

Treatment

As diabetes is a systemic disease, optimal control of blood sugar as well as blood pressure and cholesterol levels are still very important in the treatment of diabetic retinopathy. However, progression of retinopathy may occur despite all medical efforts. If diabetic retinopathy is detected early, treatment with laser photocoagulation may stop continued damage. Even in the advanced stages of the disease, laser treatment can reduce the chance that a patient will have severe visual loss.

Laser treatment is used to seal or obliterate the abnormal leaking blood vessels. This procedure focuses a powerful beam of laser light onto the damaged retina. Small bursts of the laser energy seal leaking vessels and form tiny scars inside the eye. The scars reduce new vessel growth and cause existing ones to shrink and close. Laser treatments are usually carried out in an outpatient setting.

Laser treatment for PDR(right) and laser scars(left)

In more advanced cases where there is significant bleeding or scar tissue formation, a surgical procedure called vitrectomy may be undertaken to clear the blood and remove the scar tissue. More recently, the use of anti-VEGF drugs in the management of diabetic eye disease has been described and there are extensive studies being conducted worldwide to establish its effectiveness in this disease. These new drugs essentially are injected directly into the eye and help make the abnormal vessels shrink and close. (Vitrectomy will be discussed further).

Advanced diabetic eye disease